1. Field of the Invention
The present invention relates to ordnance and more particularly to methods for controlling the trajectories of gun launched projectiles.
2. Brief Description of the Prior Art
In the firing of gun launched projectiles, a phenomenon known as dispersion in which a scattered pattern of hits of shots fired from the same gun with the same firing data will often result. A major contributor to such dispersion is another phenomenon known as "jump" which is discussed in detail below but which may, for example, result from motion imparted to the projectile by the motion of the gun itself by way of recoil. While the correction of jump induced dispersion would be desirable in indirect fire area weapons, it is particularly desirable in direct fire weapons such as tank munitions where first round hits on a target may often be critical.
The introduction of armor-piercing fin-stabilized discarding sabot (APFSDS) kinetic energy ammunition has yielded large improvements in the terminal effectiveness of tank gunnery. By launching a massive high fineness ratio rod at hypervelocity, it became possible to deliver tremendous energy on the target with unprecedented accuracy. The high velocity and resultant short time of flight to target of the APFSDS allows extremely flat trajectories which are insensitive to contributors to inaccuracy such as meteorological conditions, ranging error, velocity variations, and the like.
Since the fielding of the first generation APFSDS ammunition, a number of new generations of APFSDS ammunition have been developed. With each new generation of ammunition, the armor penetration capability has been increased. These increases in armor penetration have been achieved mainly by increasing the mass and fineness ratio of the penetrator rods. Improvements in ammunition structural design and propulsion systems enable these more massive penetrators to be launched at velocities equal to or greater than those of the original APFSDS ammunition.
In order for APFSDS ammunition to be fired effectively to longer distances than current engagement ranges, its delivery accuracy must be improved. If substantial improvements to accuracy are sought, the major contributors to delivery system inaccuracy must be addressed. When the delivery inaccuracy of a tank main armament system is broken down into its component sources, "jump" is found to be a major contributor. In the present report, "jump" refers to a launch induced veering of the trajectory from the expected flight path based on the static pointing direction of the gun muzzle. Jump itself can be broken down into a number of components, one of which is aerodynamic jump. These components are described in further detail in the following references:
Plostins, P., "Launch Dynamics of APFSDS Ammunition," Ballistic Research Laboratory, Aberdeen Proving Ground, Md., BRL-TR-2595, October 1984. PA1 Plostins, P., White, C. O., "The Transitional Ballistics, Aeroballistics and Jump of a 25mm-AP Training Projectile with Base Bleed," Proceedings of the Tenth International Symposium. on Ballistics, American Defense Preparedness Association, 1987. PA1 Plostins, P., Celmins, I., Bornstein, J., Diebler, J. E., "The effect of Sabot Front Borerider Stiffness on the Launch Dynamics of Fin-Stabilized Kinetic Energy Ammunition," Ballistic Research Laboratory, Aberdeen Proving Ground, Md., BRL-TR-3047, October 1989. PA1 Schmidt, E. M., Bornstein, J. A., Plostins, P., Haug, B., Brosseau, T. L., "Jump From M1A1 Tank," Ballistic Research Laboratory, Aberdeen Proving Ground, Md., BRL-TR-3144, September 1990 (hereafter "Schmidt").